Sonography in Obstetrics

Fetal biparietal diameter measurements were obtained simultaneously by gray scale and bistable ultrasonography. The bistable presentation was measured from leading edge to leading edge, while the gray scale presentation was measured from leading point to leading point and middle to middle of the band of echoes defining the fetal head. Statistical analysis of 50 patients demonstrated good reproducibility of the biparietal diameter measurement by each method and intraobserver variation fell well within the acceptable range. In all but one patient differences in measurements between observers and measurement methods were trivial and of no clinical significance. In the patients in whom there was a statistically significant difference, the variability was from 1 to 2 mm with the exception of one patient in whom the variability was about 4 mm.

Gray scale measurement of biparietal diameter

Lawson

Albarelli

Greenhouse

et al. 1977

False placenta previa: A clinical observation

Lees

Teates

1978

Analysis of biparietal diameter as an accurate indicator of gestational age

Kurtz

Wapner

Kurtz

et al. 1980

115

To date, there have been 25 studies attempting to correlate biparietal diameter and gestational age; of these, 17 meet specific criteria and thus are included in this evaluation. Although all studies have shown an increase in biparietal diameter with advancing gestational age, between 17 wk and term there is a discrepancy of approximately 3 wk. In this evaluation the charts are compared and the variations analyzed. An ideal table is constructed by combining the mean gestational age, calculated from a statistical analysis, and the variation at each millimeter point, determined by comparison of all the studies. It is hoped that this new 90% composite table, which consists of a range of gestational ages in weeks for each biparietal diameter, will not only provide more realistic indications of fetal age but also will serve as a reminder to sonographers, obstetricians, and patients of the relative accuracy and variations of biparietal diameter measurements.